Hydraulic fluid circuit

ABSTRACT

A hydraulic circuit having one or more pumps adjacent motor means in a machine with hydraulic motors which are supplied by the circuit being located in a relatively remote location from the pumps. A control valve is associated with each hydraulic motor and includes a return line in communication with a first hydraulic fluid tank. An assembly of one or more pumps for delivering fluid under pressure to the control valves is located adjacent the motor means and is driven by the motor means. A second hydraulic fluid tank is associated with the pump assembly, the second tank providing fluid to the pumps and being in communication with the first tank by a return conduit for delivering fluid from the first tank to the second tank. To prevent rupture of the first tank, a baffle is preferably arranged within that tank to assure a constant air pocket above the fluid.

United States Patent [72] Inventors Thomas H. Geselbracht Joliet; David S. Vinton, Morton, both of, Ill. [21] Appl. No. 834,776 [22] Filed June 19, 1969 [45] Patented Sept. 14, 1971 [73] Assignee Caterpillar Tractor Co.

Peoria, III.

[54] HYDRAULIC FLUID CIRCUIT 11 Claims, 2 Drawing Figs.

[52] US. Cl 60/52 HE, 92/142,180/11, 214/140 [51] Int. Cl ..F15b 15/18, Fl5b 1/06 [50] Field of Search 60/52 HE; 91/414; 92/142; 180/11 [56] References Cited UNITED STATES PATENTS 3,222,865 12/1965 Miller 60/52 l-IE 3,222,866 12/1965 Lehmann 60/52 HEX 3,234,855 2/1966 Freedyetal....

ABSTRACT: A hydraulic circuit having one or more pumps adjacent motor means in a machine with hydraulic motors which are supplied by the circuit being located in a relatively remote location from the pumps. A control valve is associated with each hydraulic motor and includes a return line in communication with a first hydraulic fluid tank. An assembly of one or more pumps for delivering fluid under pressure to the control valves is located adjacent the motor means and is driven by the motor means. A second hydraulic fluid tank is associated with the pump assembly, the second tank providing fluid to the pumps and being in communication with the first tank by a return conduit for delivering fluid from the first tank to the second tank. To prevent rupture of the first tank, a baffle is preferably arranged within that tank to assure a constant I air pocket above the fluid.

18 I9 I i g 4-2 I I I TILT LIFT CYLINDERS CYLINDERS 52 PATENTEDSEPI 4|s1| SHEET 2 [IF 2 INVENTORS GESELBRACHT VINTON ATTORNEYS THOMAS DAVID S.

dling vehicle such as a bucket loader having motor means for." an engine on one articulated section and implements powered by hydraulic motors on the other articulated section. In such an environment, it is desirable to locate pumps for the circuit closely adjacent the engine from which they are driven. In the prior art, a hydraulic fluid tank or reservoir is commonly located adjacent the pumps with hydraulic fluid under pres sure being communicated to the remote hydraulic motors and' exhaust fluid from the motors being returned to the tank.

When control valves for regulating fluid flow to the motors are located within the hydraulic fluid tank, as is common to place the control valves in a protective environment, numerous high-pressure supply lines and low-pressure return lines are necessary to properly communicate the tank and pumps with the hydraulic motors. The arrangement of such circuits is particularly complicated on articulated vehicles of the type mentioned above since each of the lines must cross the articulated axis of the vehicle and accordingly must include a swivel joint.

The present invention substantially minimizes these problems and simplifies the hydraulic circuit through the use of two hydraulic fluid tanks. One of the tanks is associated with the hydraulic pump or pumps while the other tank is associated with one or more remotely located hydraulic motors and regulating control valves.

In such a hydraulic circuit, one of the tanks commonly has.

inlet means for receiving fluid under pressure, for example,-

from the hydraulic motors supplied by the circuit. The tank also has outlet means through which fluid exits the tank. Normally, the tank is maintained in a condition where it is partly filled with fluid and has an air pocket above the fluid. Surges of fluid into the tank from the inlet means are normally prevented from rupturing the tank by the air pocket which tends to absorb any increased pressures. However, during operation, air commonly tends to leak out of the tank, for example, through gasket material used to close the tank particularly under high-pressure conditions caused by the fluid surges. If all of the air in the tank leaks into the atmosphere and the tank becomes filled with fluid, high pressures caused by subsequent fluid surges may tend to damage or rupture the tank.

To solve this problem, the present invention contemplates the use of baffle means for maintaining an air pocket in the tank and preventing leakage of the air.

The manner in which the present invention fulfills these purposes is illustrated by the following description wherein additional objects and advantages of the invention are also believed to be made apparent. The invention is described below having reference to the accompanying drawings.

In the drawings:

FIG. 1 is a schematic representation of the present hydraulic circuit with various components of the circuit being shown in section; and

FIG. 2 is a side view in elevation of an articulated vehicle employing the present hydraulic circuit.

The present invention is described with particular reference to an articulated vehicle of the type illustrated in FIG. 2. However, it will be apparent that the hydraulic circuit may be employed in other vehicles or machines which are not necessarily articulated but wherein motor means such as an engine for driving pumps of the circuit is located remotely from hydraulic motors supplied by the circuit.

Momentarily referring to FIG. 2, an articulated vehicle 11 for which the present hydraulic circuit is particularly contemplated has two sections 12 and 13 joined together by an articulated joint indicated at 14. For purposes of an example, the vehicle is illustrated as a bucket loader having a bucket 16 pivotally supported by one or more lift arms such as that indicated at 17. The position of the bucket is controlled by hydraulic tilt motors, one of which is indicated at 18, and hydraulic lift motors, one of which is indicated at 19. Each tilt motor is interconnected between the vehicle and the bucket by tilt linkage generally indicated at 21. Each hydraulic lift motor is pivotally interconnected between the vehicle and one of the lift arms 17.

The tilt motors and lift motors together with the bucket 16 are commonly supported by one of the articulated sections, for example that indicated at 13. An engine 22 for driving the vehicle is commonly located on the other articulated section 12.

When a hydraulic circuit of the type illustrated ingreater detail in FIG. 1 is adapted to such a vehicle, it is desirable that the hydraulic pumps be located closely adjacent the engine 22 by which they are driven. Accordingly, a cluster arrangement 23 of hydraulic pumps is shown adjacent the engine 22 upon the articulated section 12.

The present invention is believed to substantially simplify construction of a hydraulic circuit for properly interconnecting the pump cluster 23 with the hydraulic motors such as those indicated at 18 and 19. A hydraulic circuit constructed according to-the present invention is illustrated in FIG. 1 to which reference is now made. Components of the circuit in FIG. 1 are divided into two groups by a section line indicated at 31. When the circuit is adapted to a vehicle of the type illustrated in FIG. 2, one group indicated generally at 12' and including those components to the left of the section line 31 in FIG. 1 are arranged upon the articulated vehicle section 12 including the engine 22. Another group indicated at 13' and generally including those components to the right of the section line 31 in FIG. 1 are arranged upon the other articulated section 13 which also supports the bucket implement 16. As illustrated in FIG. 1, the pump cluster 23 includes two doublesectioned pumps 32 and 33. Fluid under pressure from the pumps 32 and 33 is selectively directed to the hydraulic motors 18 and 19 by control valves 34 and 36 respectively. The circuit also includes a first hydraulic fluid tank or reservoir 37 which receives fluid from the control valves 34, 36 and a second hydraulic fluid tank 38 from which fluid is drawn into the pumps 32 33 by an inlet conduit 39.

To describe various components of the circuit in greater detail, the control valves are of a type suitable for immersion in hydraulic fluid. Accordingly, the control valves 34, 36 are shown within the first tank 37. The tank 37 has a generally low, wide profile so that the control valves may be arranged in generally horizontally relation adjacent the bottom of the tank.

Fluid under pressure from the pump 32 is combined in a manifold 41 from where it passes into an outlet conduit 42. The conduit 42 is also in communication with the control valve 34. The valve 34 includes a spool, generally indicated at 43, which may be positioned to direct fluid from the conduit 42 into either end of the hydraulic motor 18 by respective conduits 44 and 46. The spool 43 may also be positioned so that fluid from the conduit 42 passes directly into a fluid return line 47 which communicates the control valve 34 with the first tank 37. When the control valve is adjusted to direct fluid into either end of the motor 18, exhaust fluid from the other end of the motor 18 is also delivered by the control valve into the return conduit 47.

The other pump 33 is similarly in communication with the control valve 36 by a manifold 51 and a high-pressure outlet conduit 52. The control valve 36 includes a control spool generally indicated at 53. The control valve 36 is similarly in communication with both ends of the hydraulic motor 19 through respective conduits 54 and 56 and with the first tank 37 by means of the same fluid return line 47.

The first tank 37 is in communication with the second tank 38 by means of a return conduit indicated at 61. The return conduit 61 is in communication with the first tank 37 by means of a stand pipe 62 which normally establishes the fluid level in the first tank 37. A bafile assembly 63 is arranged at one end of the return conduit 61 to prevent aeration of the fluid entering the second tank 38. A similar baffle assembly 64 is mounted on the fluid return 47 in communication with the first tank 37. Under normal operating conditions, both tanks 37, 38 are partly filled with hydraulic fluid to form air pockets in the tops of the tanks. Fluid under pressure is delivered into the first tank 37 through the fluid return 47 which tends to increase pressure in its air pocket generally indicated at 66. When the fluid level in the first tank 37 is above the top of stand pipe 62, the increased pressure causes excess fluid to flow into the second tank 38. Thus, pressure within the first tank 37 will normally be slightly higher than air pressure in the second tank 38 by the differential pressure drop required to transmit fluid through the return conduit 61. The two tanks 37, 38 are relatively positioned so that the normal fluid level in the first tank 37 is somewhat higher than the fluid level in the second tank 38.

Since all return fluid form the control valves 34, 36 is delivered to the first tank 37, surges of fluid, for example exhausted from the hydraulic motors l8 and 19 may substantially increase the pressure in the first tank. These pressure surges tend to cause air within the tank 37 to leak to the atmosphere, particularly across the gasket material 67 which seals the cover 68 in place atop the first tank 37. if this leakage is permitted to continue, the first tank 37 could become entirely filled with fluid. In that event, subsequent fluid surges into the tank 37 could rupture the tank.

To prevent this from happening, the present invention contemplates baffle means 71 forming a region 72 at the top of the tank 37. The baffle 71 is preferably a cylindrical structure secured to the cover 68 and opening downwardly toward fluid within the tank 37 Since the cover 68 to which the baffle is secured is generally continuous, leakage of air from the region 72 is prevented so that a substantial air pocket is assured at the top of the first tank 37 during operation of the system. This air pocket provides a cushion for pressure surges within the tank and thereby prevents damage to the tank itself.

To commence operation of the present hydraulic circuit, hydraulic fluid is first introduced into the first tank 37 until it reaches the top of stand pipe 62. The second tank 38 is then filled with fluid to a somewhat lower level which may be determined for example by a sight gauge 73. The pumps 32, 33 are then momentarily operated so that all of the conduits and other components of the circuit are filled with fluid. The pumps are then shut down and the second tank 38 is again filled to a level somewhat lower than the fluid level determined by the stand pipe 62in the first tank 37.

The fluid may be added to the first and second tanks by means of filler caps indicated at 74 and 76 respectively. To completely prevent leakage of air from the region 72 past the filler cap 74, a cylindrical pipe 77 supporting the cap 74 is hermetically secured to the cover 68 and extends downwardly at least as far as the baffle 71.

What is claimed is:

1. A hydraulic circuit for a machine having a motor means and a hydraulic motor remotely located from the motor means of the machine, comprising at least one hydraulic pump associated in driven relation with the motor means a control valve associated with the hydraulic motor, said control valve being in communication with a fluid outlet conduit of said pump, said control valve being selectively operable to deliver fluid under pressure for operating the motor,

a first hydraulic fluid tank associated with said control valve, said first tank being in communication with a fluid return from said valve,

a second hydraulic fluid tank associated with said pump, said second tank being in communication with an inlet conduit to said pump, and a return conduit providing substantially free communication between said first and second tanks for delivering hydraulic fluid from said first tank to said second tank, said return conduit including a stand pipe in said first tank for establishing a normal fluid level therein.

2. The invention of claim 1 wherein said control valve is of a type for immersion in hydraulic fluid and said valve is disposed within said first tank.

3. The invention of claim 1 wherein the machine includes a plurality of the hydraulic motors and further comprising one of said control valves associated with each hydraulic motor.

4 The invention of claim 3 further comprising a plurality of said pumps respectively associated with said control valves.

5. The invention of claim 3 wherein said control valves are of a type suitable for immersion in hydraulic fluid, said control valves being arranged in generally horizontal relation within said first tank generally adjacent the bottom thereof.

6. The invention of claim 1 wherein said two tanks are relatively disposed upon the machine so that the fluid level is normally somewhat higher in said first tank than in said second tank.

7. The invention of claim 1 wherein the machine is a vehicle and the motor means is its engine.

8. The invention of claim 1 wherein baffle means are secured to a generally continuous portion of said first tank for maintaining an air pocket at the top of said first tank.

9. The invention of claim 8 wherein a removable cover is arranged atop said first tank and said baffle means is a cylindrical member secured to the cover and extending downwardly therefrom.

10. A hydraulic circuit for a vehicle having motor means, at least one implement and a hydraulic motor for operating the implement being remotely located from the motor means, comprising a hydraulic pump associated with and coupled in driven relation to the motor means,

a control valve hydraulically associated with the hydraulic motor, said control valve being in communication with said pump by a high-pressure fluid conduit,

a first hydraulic fluid tank associated with said control valve, said first tank being in communication with a fluid return line from said valve,

a second hydraulic fluid tank associated with said pump, said second tank being in communication with an inlet conduit for delivering hydraulic fluid to said pump, and

a return conduit substantially freely communicating said two tanks for delivering fluid from said first tank to said second tank, said return conduit including a stand pipe in said first tank for establishing a normal fluid level therein.

11. The invention of claim 10 wherein the vehicle includes a plurality of the hydraulic motors, a plurality of control valves being respectively associated with the hydraulic motors and arranged in generally horizontal relation within said first tank,

a plurality of said pump being in respective communication with said valves. 

1. A hydraulic circuit for a machine having a motor means and a hydraulic motor remotely located from the motor means of the machine, comprising at least one hydraulic pump associated in driven relation with the motor means a control valve associated with the hydraulic motor, said control valve being in communication with a fluid outlet conduit of said pump, said control valve being selectively operable to deliver fluid under pressure for operating the motor, a first hydraulic fluid tank associated with said control valve, said first tank being in communication with a fluid return from said valve, a second hydraulic fluid tank associated with said pump, said second tank being in communication with an inlet conduit to said pump, and a return conduit providing substantially free communication between said first and second tanks for delivering hydraulic fluid from said first tank to said second tank, said return conduit including a stand pipe in said first tank for establishing a normal fluid level therein.
 2. The invention of claim 1 wherein said control valve is of a type for immersion in hydraulic fluid and said valve is disposed within said first tank.
 3. The invention of claim 1 wherein the machine includes a plurality of the hydraulic motors and further comprising one of said control valves associated with each hydraulic motor. 4 The invention of claim 3 further comprising a plurality of said pumps respectively associated with said control valves.
 5. The invention of claim 3 wherein said control valves are of a type suitable for immersion in hydraulic fluid, said control valves being arranged in generally horizontal relation within said first tank generally adjacent the bottom thereof.
 6. The invention of claim 1 wherein said two tanks are relatively disposed upon the machine so that the fluid level is normally somewhat higher in said first tank than in said second tank.
 7. The invention of claim 1 wherein the machine is a vehicle and the motor means is its engine.
 8. The invention of claim 1 wherein baffle means are secured to a generally continuous portion of said first tank for maintaining an air pocket at the top of said first tank.
 9. The invention of claim 8 wherein a removable cover is arranged atop said first tank and said baffle means is a cylindrical member secured to the cover and extending downwardly therefrom.
 10. A hydraulic circuit for a vehicle having motor means, at least one implement and a hydraulic motor for operating the implement being remotely located from the motor means, comprising a hydraulic pump associated with and coupled in driven relation to the motor means, a control valve hydrauLically associated with the hydraulic motor, said control valve being in communication with said pump by a high-pressure fluid conduit, a first hydraulic fluid tank associated with said control valve, said first tank being in communication with a fluid return line from said valve, a second hydraulic fluid tank associated with said pump, said second tank being in communication with an inlet conduit for delivering hydraulic fluid to said pump, and a return conduit substantially freely communicating said two tanks for delivering fluid from said first tank to said second tank, said return conduit including a stand pipe in said first tank for establishing a normal fluid level therein.
 11. The invention of claim 10 wherein the vehicle includes a plurality of the hydraulic motors, a plurality of control valves being respectively associated with the hydraulic motors and arranged in generally horizontal relation within said first tank, a plurality of said pump being in respective communication with said valves. 